Light measurement apparatus with resiliently biased sheath for defining light-tight enclosure and related method

ABSTRACT

Light measurement apparatus includes an elongate member which has at one end thereof light emitter(s) and light detector(s). At least the end of the elongate member that has the light emitter(s) and light detector(s) is surrounded by a resiliently biased sheath. In use, when the elongate member is applied to a surface to take a reading, the sheath defines a light-tight enclosure. A related method for determining intensity and/or color of a colored spot on a surface of a test site uses the light measurement apparatus. The method includes bringing the end of the elongate member into contact with the surface, pressing the resiliently biased sheath towards the surface to define a light-tight enclosure, and measuring the intensity and/or color of the colored spot on the surface.

FIELD OF THE INVENTION

This invention relates to light measurement apparatus, in particular,though not exclusively, to colour and/or intensity measurement apparatusfor use with for example a biomedical diagnostic test card.

BACKGROUND OF THE INVENTION

In recent years there have been developed test cards, e.g. solid phaseimmunoassay test cards, for biomedical diagnostic purposes. Such testcards are normally provided with one or more test sites, normally only afew millimeters (eg. about 5 millimeters) wide, to which a liquid sample(e.g. blood or serum) is applied. The test sites are designed to changecolour in response to the presence and concentration of a particularcomponent (e.g. a certain protein) in the liquid sample.

This colour change can, at least to a certain extent, be detected andmeasured by eye, by for example comparing a treated test site with areference colour chart. Such visual techniques are, however, clearlyunsatisfactory when it is desired to produce an accurate reliablemeasurement. To obtain reliably highly accurate measurements, aninstrumental system is sought.

Measurement of colour, colour spectra and colour intensity of an opaquesurface is performed by analyzing the light reflected from the surfacewhen exposed to a defined light. It is essential that the surface areato be measured and the detection system are not exposed to externallight during measurements, and light shielding of the mechanism istherefore provided. This is particularly critical if weak light sourcessuch as light emitting diodes (LEDs) are used rather than strong sourcessuch as xenon arc lamps or the like. It is also important that the lightemitter and the light detector have defined positions relative to thesurface to be measured.

Conventional instruments for analyzing surface colours tend to be largeand heavy, thus not readily transportable, or smaller but stillinflexible in use. Attempts to develop more versatile, smalltransportable systems have been made, but to date no known system meetsall the requirements to overcome the problems of the prior art.

SUMMARY OF THE INVENTION

According to the present invention there is provided light measurementapparatus comprising an elongate member, said elongate member having atone end thereof light-emitting means and light-detecting means, at leastthe end of said elongate member provided with said light-emitting meansand said light-detecting means being surrounded by a resiliently biassedsheath whereby in use when said elongate member is applied to a surfaceto take a reading said sheath defines a light-tight enclosure.

Preferably, the light-emitting and light-detecting means may compriseelectronic components such as photodiodes, phototransistors or the likewhereby the dimensions at the end of the member (i.e. the "tip") may besmall so that the apparatus may be applied to a small surface area. Theprovision of a sheath to define a light-tight enclosure enables a lowintensity light source to be used as the light-emitting means, e.g. alight-emitting diode (LED).

The light-emitting means may comprise means for emitting broad spectrumlight or light of limited wavelength ranges. The use of two or morenarrow band emitters will allow simple spectral analysis to beperformed. Such a possibility is particularly advantageous when it isdesired to measure concentration ratio(s) of two or more components onthe test site which absorb light of different wavelength bands/regions.In this latter arrangement, two or more separate light sources may beprovided, e.g. two or more LEDs, or alternatively switchable filtermeans may be provided to a single light source. Since absorption spectrafrom coloured surfaces always are of a broad-band nature, thesignal-to-noise (S/N) ratio can be improved during measurements by usingbroad-band light emitters which coincide with the absorption range.

The sheath is preferably adapted to be slidable between the position inwhich it defines a light-tight enclosure, and a position in which theend of the elongate member is exposed. This facilitates initialapplication of the apparatus to a small area, after which the sheath maybe moved to define the light-tight enclosure. Preferably, indeed, thesheath may be biased, e.g. by resilient means such as a spring, into aposition to expose the end of the elongate member. The end of the sheathadjacent the end of the elongate member may be provided with a sealingring to further ensure a light-tight seal.

The operation of the apparatus to effect a measurement may simply beleft for an operator's command. Preferably, however, the tip of theelongate member is provided with a light sensor (e.g. a phototransistoror the like) to be located within the light-tight enclosure. Thelight-sensor can be arranged to detect when it is sufficiently darkwithin the enclosure for a reliable accurate reading to be taken and viacontrol circuitry may then cause a measurement to be taken.

In addition to defining a light-tight enclosure, the provision of asheath member also has the advantage of helping to ensure that theapparatus is operated in the correct orientation, i.e. perpendicular tothe surface to be measured.

It is also particularly preferred that the light-emitting means and thelight-detecting means are arranged asymmetrically with respect to eachother, to avoid any problems with light being directly reflected off aglossy surface. Indeed viewed from another aspect the invention provideslight measurement apparatus comprising an elongate member having at oneend thereof light-emitting means and light-detecting means, saidlight-emitting means and said light-detecting means being asymmetricallyarranged with respect to the central axis of said elongate member.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described by way of exampleand with reference to the accompanying drawings, in which:

FIG. 1 is a sectional side view of apparatus according to an embodimentof the invention;

FIG. 2 is a cross-section through the apparatus in the region of the tipthereof;

FIG. 3 is a view along line III--III; and

FIG. 4 is a view along line IV--IV.

DESCRIPTION

Referring first to FIG. 1 there is shown therein an elongate pen-likemember 1 comprising a cylindrical housing 2. One end of the housing 2 isprovided with an aperture for receiving a cable 3 by means of which thelight-emitting, -detecting and -sensing elements (to be described below)may be operatively connected to a remote control unit such as amicroprocessor (not shown). The apparatus may include light intensitymeasurement circuitry of the type disclosed in our co-pendingapplication entitled "Light Measurement", the contents of which areincorporated herein by reference. The application referred to in thepreceding sentence is International Patent Application No.PCT/GB93/01356 which has an international filing date of Jun. 29, 1993,which published as WO94/00742 on Jan. 6, 1994, and which is now lapsedbecause the national phase was not entered in any country.

The other end of the cylindrical housing 2 is closed by a base memberand a conical tip member 4. The conical tip member 4 is formed with ahollow central chamber 5 within which are located light-emitting meansin the form of a light-emitting-diode (LED) 6, and light-detecting meansin the form of a photodiode 7. The chamber 5 opens to the exterior ofthe tip member 4 at the apex thereof which defines a measurementlocation which is positioned on the central longitudinal axis of thehousing 2. Locating the LED 6 and photodiode 7 recessed within theconical tip member 4 both helps protect them from accidental damage andshields them partly from stray light.

Surrounding the lower half of the housing 2 is a cylindrical sheath 8 oflight impermeable material, around the lower end of which is provided anannular sealing ring 9 formed for example of a resilient elastomericmaterial. A spring 10 is located between an annular shoulder 11 formedat a lower end of the housing 2 and an inwardly directed annular rim 12formed at the upper end of sheath 8. The spring 10 normally biases thesheath 8 upwardly out of the position of FIG. 1 to expose the conicaltip member 4. In use, the tip member 4 is applied to the surface to bemeasured and subsequently the sheath 8 is moved downwardly against thespring bias until the sealing ring 9 contacts the surface around theregion to be measured. There is thus defined a light-tight enclosurewithin which are received the surface to be measured, and thelight-emitting and detecting means.

A bore 13 is formed in the conical member 4 and the base of the housing2 at the end of which remote from the exterior is provided aphoto-transistor 14. The phototransistor 14 is adapted to sense when thelight within the light-tight enclosure is below a minimum level for anaccurate measurement to be taken. The phototransistor 14 then sends asignal to the control means to cause the LED 6 to operate to take ameasurement.

As can be seen from FIGS. 2, 3 and 4, the LED 6 and photodiode 7 arepositioned asymmetrically with respect to each other and the centrallongitudinal axis of the housing whereby if the apparatus is applied toa glossy surface, directly reflected light from the LED 6 cannot bereceived by the photodiode 7.

Although the invention has been described with particular reference tocolour measurement, it will be appreciated that the range ofapplications is wider and, for example, with suitable programming of thecontrol means, the invention could be applied to a bar-code reader, e.g.for up-dating the apparatus with new test data.

It should also be understood that although reference is made in thisspecification to the term "light", it is not intended that the inventionbe limited to visible light, but rather the invention may also extend tothe non-visible parts of the electromagnetic spectrum.

In addition to solid phase immunoassay test cards, the apparatus may ofcourse also be used to measure relative colour intensity in otheranalytical methods giving rise to coloured responses, e.g. dot/spotimmunoassays and electrophoretic blotting systems.

What is claimed is:
 1. Light measurement apparatus comprising anelongate member (1), said elongate member having at one end thereoflight-emitting means (6) and light-detecting means (7), at least the endof said elongate member with said light-emitting means (6) and saidlight-detecting means (7) being surrounded by a resiliently biasedsheath (8) whereby in use when said elongate member (1) is applied to asurface to take a reading said sheath (8) is in a position in which itdefines a light-tight enclosure.
 2. Apparatus as claimed in claim 1 inwhich the light-detecting means is a photodiode.
 3. Apparatus as claimedin claim 1 or claim 2 in which the light-emitting means is alight-emitting diode.
 4. Apparatus as claimed in claim 1, in which atleast two light-emitting means are provided to emit light at differentwavelengths.
 5. Apparatus as claimed in claim 1, in which theresiliently biased sheath is slidable between the position in which itdefines the light-tight enclosure, and a position in which the end ofthe elongate member is exposed.
 6. Apparatus as claimed in claim 5 inwhich an end of the sheath adjacent the end of the elongate member isprovided with a sealing ring.
 7. Apparatus as claimed in claim 1, inwhich the elongate member is in a perpendicular orientation relative tosaid surface when in the sheath defines the light-tight enclosure. 8.Apparatus as claimed in claim 1, in which a tip of the elongate memberis provided with a light sensor within the light-tight enclosure andcontrol means whereby light measurement is only taken by thelight-detecting means when it is sufficiently dark within thelight-tight enclosure for a reliable accurate reading to be taken. 9.Apparatus as claimed in claim 1, in which the light-emitting means andlight-detecting means are arranged asymmetrically with respect to acentral axis of the elongate member.
 10. A method of determining atleast one of intensity and color of a colored spot on a surface of atest site by using apparatus comprising an elongate member which has atone end thereof light-emitting means and light-detecting means whereinthe end with the light-emitting means and the light-detecting means issurrounded by a resiliently biased sheath, the methodcomprising:bringing the end of the elongate member with thelight-emitting means and light-detecting means into contact with thesurface; pressing the resiliently biased sheath towards the surface todefine a light-tight enclosure; and measuring at least one of theintensity and color of the colored spot on the surface.
 11. The methodof claim 10 wherein the colored spot is about 5 millimeters in size. 12.The method of claim 10 wherein the colored spot is derived from a solidphase immunoassay.
 13. The method of claim 10 wherein the colored spotis derived from a dot/spot immunoassay.
 14. The method of claim 10wherein the colored spot is derived from an electrophoretic blottingsystem.